Cellular adaptations after ionizing radiation: the effects of amifostine and exercise

The aim of the present dissertation was to study the radiation toxicity and its protection of healthy tissues in male mice. Initially, we investigated the dose-dependent protection afforded by amifostine against lethal fractionated radiation in mice. Then we studied the ‘’'autophagic flux’’ in normal tissues under different stress conditions such as: i. starvation (induction of autophagy), ii. chloroquine (inhibition of autophagy) and iii. ionizing radiation. Then, we studied the affects of ionizing radiation in autophagic response in lung and liver tissues of mice, as well and the cytoprotective effect of the amifostine on radiation-induced dysfunctional autophagy. Finally, we investigated the role of exercise on the homeostatic mechanism of autophagy after exposure to ionizing radiation in mice. The results of the first study showed that the minimum dose of amifostine to achieve 100% survival in animals after a dose of 2x6 Gy and 3x6 Gy is 25 mg/kg/day and 75 mg/kg/day, respectively. Also the 200-300 mg/kg/day amifostine provided significant protection, after 4x6 Gy as 11 out of 18 mice survived 30 days of recording. The results of the second study shown that the LC3A protein follows discrete patterns of LC3A-I and LC3A-II changes in liver, lung, kidney and heart tissues of mice, whereas the LC3B protein didn’t follow the same pattern under stressor conditions. We conclude that the endogenous LC3A processing is a major marker of autophagy flux in mouse model. The results of the third study showed that the mechanism of autophagy deregulated after 6Gy gamma radiation in normal lung cells. Deregulation was characterized by reduced LC3A mRNA transcription and accumulation of LC3A, and p62 protein, either due to defective formation of autophagosomes (lysosome fusion) or disruption of the mechanisms of degradation of autophagy-lysosomes. The results of the fourth study showed that exercise increases the levels of LC3A after irradiation in the liver and lung tissues of mice. Also, exercise failed to protect against lethal dose 2x6Gy of fractionated radiation in mice. In conclusion the present thesis supports the idea that ionizing radiation causes dysfunctional autophagy and this might be the concept of the mechanism for the radiation-indueced cell death toxicity